Probing Leptogenesis

TL;DR

This paper reviews experimental approaches to test leptogenesis mechanisms, focusing on low-scale scenarios like ARS and discussing how to falsify high-scale leptogenesis through washout process observations.

Contribution

It provides a comprehensive overview of experimental tests for leptogenesis, including new insights into falsification methods for high-scale scenarios.

Findings

ARS leptogenesis can be tested at neutrino experiments and colliders.

Falsification of high-scale leptogenesis is possible via washout process measurements.

Extended models offer additional testability avenues.

Abstract

The focus of this chapter lies on the possible experimental tests of leptogenesis scenarios. We consider both leptogenesis generated from oscillations, as well as leptogenesis from out-of-equilibrium decays. As the Akhmedov-Rubakov-Smirnov (ARS) mechanism allows for heavy neutrinos in the GeV range, this opens up a plethora of possible experimental tests, e.g. at neutrino oscillation experiments, neutrinoless double beta decay, and direct searches for neutral heavy leptons at future facilities. In contrast, testing leptogenesis from out-of-equilibrium decays is a quite difficult task. We comment on the necessary conditions for having successful leptogenesis at the TeV-scale. We further discuss possible realizations and their model specific testability in extended seesaw models, models with extended gauge sectors, and supersymmetric leptogenesis. Not being able to test high-scale leptogenesis directly, we present a way to falsify such scenarios by focusing on their washout processes. This is discussed specifically for the left-right symmetric model and the observation of a heavy $W_R$, as well as model independently when measuring $\Delta L = 2$ washout processes at the LHC or neutrinoless double beta decay.